Photocatalytic upgrading of biomass-derived carbohydrates and glycerol into lactic acid (LA) offers a sustainable route to biodegradable plastics and avoids the high temperature/pressure and stoichiometric bases required by traditional thermocatalysis. However, aqueous photoreforming at neutral pH suffers from poor selectivity because the key intermediate, pyruvaldehyde (PYA), undergoes multiple redox reactions in parallel with intramolecular disproportionation to produce LA. By introduction of effective Lewis-acid sites (unsaturated Ti4+), a Cannizzaro-type reaction is enabled with cascade photooxidation and 1,2-hydride shift for highly selective production of LA over proton-coupled electron transfer (PCET) intermediates and •OH-overoxidized products. Upon irradiation, the Lewis-acid sites modulate photooxidation and intermediate binding, whereas the plasmonic Au nanoparticles induce localized heat to promote the rate-limiting 1,2-hydride shift, thus preventing overoxidation. The overall cascade leads to >90% LA selectivity, a 3.4-fold increase from solely photocatalytic processes, and an unprecedented productivity of 130.8 mmol g-1 h-1 under ambient conditions. This work highlights the potential of multifunctional catalysts to steer complex and parallel reaction networks toward efficient solar biorefineries.
Zhang et al. (2026) studied this question.